🔺🔥2.2 Adaptations For Gas Exchange Flashcards
What is a respiratory surface
The site of gas exchange e.g respiratory surface of a fish = gills and human = alveoli in the lungs
What is gas exchange
The diffusion of gases down a concentration gradient across a respiratory surface, between an organism and it’s environment
What is the respiratory surface in leaves
Spongy mesophyll cells in leaves
What is the respiratory surface in insects
The tracheae
What must a respiratory surface have/be for efficient gas exchange
- large surface area to volume ratio
- thin so diffusion pathway is short
- permeable do that respiratory gases diffuse easily
- mechanism to produce a steep diffusion gradient across surface by bringing oxygen/removing co2 rapidly
Give an example of a unicellular organism
Amoeba
Why can unicellular organisms complete only simple diffusion
Because:
- large surface area:volume ratio
- cell membrane is thin so diffusion into cell is rapid
- a single cell is thin :: diffusion distance inside cell is short
Why is unicellular organisms being thin/large surface area beneficial
- can absorb enough oxygen across cell membrane to meet respiratory demands
- can remove Co2 fast to prevent building up a high concentration and making cytoplasm too acidic for enzymes to function
Why are multicellular organisms less efficient for gas exchange?
Lower surface area to volume ration so simple diffusion across cell membrane does not meet demands
Name an organism that has overcome the problem of their size to diffuse gas simply
Flatworms because they have a large surface area to volume ratio :: no part of the body is far from the surface to diffusion paths are short
Which is more efficient for gas exchange, a spherical or cylindrical organism
Cylindrical organism as it has a larger surface area to volume ratio
Define metabolic rate
The rate of energy expenditure by the body
Define terrestrial organism
An organism that lives on land e.g earthworm
Describe the gas exchange in an earthworm compared to flatworm
-cylindrical so surface area to volume ratio is smaller than flatworms :: can’t simply diffuse but larger than compact organism of same volume
What is the respiratory surface of earthworm and describe why this is important
- Skin is the respiratory surface, kept moist by secreting mucus
- need for moist surface restricts earthworm to damp soil environment
What do earthworms contain that flatworms don’t
A circulatory system containing haemoglobin which has an affinity for oxygen carrying but around the body and away from surface maintaining diffusion gradient
Why does the earthworm have a low oxygen requirement
Because it’s slow moving and has a low metabolic rate
This means oxygen diffuses across skin into the blood capillaries beneath
Name another aspect maintaining concentration gradient in the earthworm
Carbon dioxide is carried in the blood and diffuses out across the skin, down concentration gradient
Why do multicellular animals e.g mammals and insects have special features not seen in unicellular organisms
- generally have a higher metabolic rate :: need to deliver more oxygen to respiring cells
- as size and the specialisation of cells increases tissues and organs become more interdependent
- must actively maintain concentration gradient across respiratory surface
- respiratory surfaces must be thin so short diffusion pathway
What problems could arise due to thin respiratory surfaces?
What adaptation protects them?
Fragile and could easily be damaged
As they are inside an organism, lungs of a mammal and gills of a fish protect them
How to larger organisms maintain a concentration gradient?
Move environmental medium, air or water, and in larger animals the internal medium the blood. (Ventilation mechanisms)
What major problems did terrestrial organisms face when colonising land from the sea?
- water evaporates from body surface resulting in dehydration
- gas exchange surfaces must be thin and permeable with a large surface area but water molecules are very small and :: pass through gas exchange surfaces meaning surfaces aren’t always moist
How did animals evolve so they could first survive on land
Gills could not function on land but the tracheae of insects and the lungs of vertebrates do
How to lungs minimise water loss,
Name 2 simple advantages
Lungs are internal, minimising water and heat loss
They allow gas exchange with air and allow animals to be active
Give some examples of amphibians
Frogs, roads and newts
Name some facts about the amphibians skin
- Skin is moist and permeable
- Located above a developed capillary network
How does gas exchange occur in amphibians
Gas exchange takes place through the skin, and when animal is active, in the lungs also
Name some examples of reptiles
Crocodiles, lizards and snakes
Name an an adaptation that reptiles have to improve gaseous exchange
Their Lungs have a more complex internal structure than other mammals e.g amphibians and therefore increased surface area for gas exchange
What 3 things so all advance multicellular organisms have for gas exchange
1) ventilation mechanism
2) internal transport system e.g circulatory system
3) respiratory pigment (haemoglobin) to increase oxygen carrying capacity
Why is birds having large lungs an advantage?
Advantage as large volumes of oxygen can be processed as flight requires a lot of energy (metabolically active)
Describe ventilation method in birds
- don’t have a diaphragm
- ribs and flight muscles ventilate their lungs more efficiently than methods used by other vertebrates
Define ventilation
Bringing gases to or from a gas exchange surface; only occurs In some organisms
Name 3 characteristics of all gills
- One way current of water, kept flowing by specialised ventilation mechanism
- Many folds, providing a large surface area over which water flows for gas exchange
- Large surface area, maintained as the density of water flowing prevent the gills from collapsing
What are the 2 main groups of fish
What is the main difference between these two groups?
Bony and cartilaginous fish
Bony fish have a skeleton of bone, cartilaginous fish have a skeleton of cartilage
Cartilaginous fish:
How many gills do cartilaginous fish have in either side?
What is this arrangement called?
Where are these visible from?
Gills in 5 spaces on each side
Arrangement = gill pouches
Visible= open to the outside at gill slits
Cartilaginous fish:
Define parallel flow
Blood and water flow in the same direction at the gill lamellae, maintaining the concentration gradient for oxygen to diffuse into the blood only up to the point where it’s concentration in the blood and water is equal (50-50)
Cartilaginous fish:
Why is the ventilation system of Cartilaginous fish less efficient than that of bony fish?
- no special mechanism to force water over gills :: must keep swimming for ventilation to occur
- blood and water travel In same direction over capillaries (parallel flow) :: blood oxygen concentration is limited to 50% of its max value
- gas exchange does not occur over whole gill Lamellae
LEARN OXYGEN DIFFUSION IN PARALLEL FLOW DIAGRAM
LEARN OXYGEN CONCENTRATION ACROSS THE GILL LAMELLA OF A CARTILAGINOUS FISH DIAGRAM
Bony fish:
What is the operculum
The covering over the gills of a bony fish
Bony fish:
Where do bony fish live?
Fresh water and Sea water
Most numerous of aquatic vertebrates
Bony fish:
Example of a bony fish?
Describe the structure of the gills in a bony fish
- Catfish
- Internal skeleton made of bone with the operculum covering its gills
Describe the process of ventilation in bony fish (taking water in)
A) mouth opens (acts as a pump)
B) operculum closes
C) floor of mouth is lowered
D) volume inside mouth cavity increases
E) pressure inside mouth cavity decreases
F) water flows in as external pressure is higher than pressure inside the mouth
Describe the process of ventilation in a bony fish (forcing water out over the gills)
A) mouth closes
B) operculum opens
C) floor of mouth is raised
D) volume inside mouth cavity decreases
E) pressure inside mouth cavity increases
F) water flows our over he gills because the pressure inside the mouth cavity is higher than in the opercular cavity and outside
How many pairs of gills to bony fish have?
What is each gill supported by?
- 4 pairs of gills
- Each gill is supported by a gill arch made of bone
Where are the gas exchange surfaces located in a bony fish?
On the gill fillents in a section called the gill lamellae
Why are gill lamellae vital for gas exchange in bony fish?
Vital as the gill filaments are held apart by water flowing between them providing a large surface area for gas exchange
Why do fish die out of water?
Out of water the gill fillaments stick together and collapse so much less surface area is exposed and not enough gas exchange occurs
Define counter current flow
Blood and water flow in opposite directions at the gill lamellae maintaining the concentration gradient and therefore, oxygen diffusion into the blood alone their entire length
Name the flow of water through a bony fish until gas exchange
Mouth cavity
Opercular cavity
Gill pouches
Flows between gill lamellae where blood in gill capillaries flows in opposite direction (counter-current flow)
LEARN COUBTER CURRENT FLOW DIAGRAM
LEARN DIAGRAM OF FISH GILLS ETC ON Pg 166
Why is counter current flow in bony fish more efficient than parallel flow In cartilaginous fish
Water always has a higher oxygen concentration than the blood in counter-current flow so oxygen diffuses into the blood along whole length of gill lamellae, removes about 80% of oxygen from water
Why is a high percentage of oxygen extraction (e.g 80% in bony fish) vital to fish?
Important to fish as water contains much less oxygen than air
LEARN OXYGEN DIFFUSION IN COUNTER-CURRENT FLOW
LEARN OXYGEN CONCENTRATION ACROSS THE GILL LAMELLAE OF A BONY FISH DIAGRAM
Statement about oxygen concentration across gill lamellae of bony fish
With increase distance along the gill lamella, the concentration of oxygen in the blood increase and that of water decreases until the concentration in blood is very high and water is very low
Describe the Carbon dioxide diffusion in cartilaginous fish vs bony fish
In cartilaginous fish carbon dioxide diffuses from the blood to the water
In a bony fish (due to counter-current system) carbon dioxide diffuses out of the blood along whole length of gill lamellae :: more efficient than the carbon dioxide loss from gills of cartilaginous fish
Name the 3 vital things gills provide
1-specialised respiratory surface, rather than using body surface
2- large surface extended by gill filaments and gill lamellae
3- an extensive network of blood capillaries, with blood carrying haemoglobin allowing efficient diffusion of oxygen into blood and carbon dioxide out
Where are the lungs located in the human breathing system
Enclosed in an airtight compartment called the thorax
Where are the pleural membranes in the human breathing system
Lone the thorax and cover each lung
What is the purpose of the pleural fluid in the human breathing system
Fluid between the membrane prevents friction between the lungs and chest cavity as the lungs move during ventilation
Where is the diaphragm, what is it’s shape and what does it do?
- The diaphragm is at the base of the thorax, a dome shaped sheet of muscle,
- It separates he thorax from the abdomen
Where are the ribs located in the human breathing system
They surround the thorax
Where are the intercostal muscles located in the human breathing system
Between the ribs
What is the trachea
A flexible airway that brings air into the lungs
What are contained insides the lungs of a human.
Branching network of tubes called bronchioles which arise from bronchi
What are at the ends of bronchioles?
Air sacs called alveoli
Why are the cartilage rings around the trachea not complete at the back?
To allow the oesophagus behind it to bulge as the bolus of food is swallowed, without meeting a hard structure which would prevent the food from moving past
How do mammals ventilate their lungs? What does this mean?
- Negative pressure breathing
- Meaning for air to enter the lungs the pressure inside the lungs must be below atmospheric pressure
Describe the stages of inspiration (inhalation)
A) external intercostal muscles contract
B) ribs are pulled upwards and outwards
C) at the same time the diaphragm muscles contract so it moves down and flattens
D) both actions increase thorax volume
E) this reduces pressure in the lungs
F) atmospheric pressure is now greater than the pressure in the lungs, so air is drawn into the lungs
Describe the process of expiration (exhalation)
A) external intercostal muscles relax
B) ribs move downwards and inwards
C) at the same time the diaphragm muscles relax, so it domes upwards
D) both actions decrease the thorax volume
E) increases pressure in the lungs
F) air pressure in the lungs is now greater than atmospheric pressure so air is forced out of the lungs
What is the main cause of air being forced out of the lungs during normal breathing?
The elastic recoil of the lungs, the lung tissue is elastic and regains it’s original shape when not being actively expanded
What is the surfactant made of? Where is it located in the human breathing system?
-The surfactant is an anti sticking mixture made out of moist secretions containing phospholipids and protein inside the surfaces of the alveoli.
What is the two main roles of the surfactant
- It allows the gases to dissolve before diffusing in/out of alveoli
- also has a low surface tension to prevent the alveoli collapsing during exhalation when air pressure is low
Why is gas exchange in the alveolus very efficient? (5)
- Large surface area:volume ratio
- Gases dissolve In the surfactant moisture lining the alveoli
- Walls made up of squamous epithelium, only one cell thick :: short diffusion pathway
- Extensive capillary network surrounds the alveoli
- Capillary walls are also only one cell thick contributing to small diffusion pathway
Why is the extensive capillary network surrounding the alveoli important
Vital for maintaining diffusion gradients as co2 is rapidly brought to the alveoli and oxygen is rapidly carried away
Why is the diffusion pathway short in the alveolus?
Because BOTH the walls of the alveoli (made of squamous epithelium cells) and capillaries are only 1 cell thick
Describe the gas exchange in the alveolus
1) deoxygenated blood enters the capillaries surrounding the alveoli
2)oxygen diffuses out of the air in the alveoli into the red blood cells in the capillary
3)carbon dioxide diffuses out of the plasma in the capillary into the air in the alveoli from where it is exhaled
(LOOK AT DIAGRAM ON PAGE 171)
Name the compositions for the % oxygen in inspired vs expired air
Why does this occur?
Inspired= 20% Expired= 16%
Occurs because oxygen is absorbed into the blood at the alveoli and used in aerobic respiration
What is the % composition of carbon dioxide in inspired vs expired air
What is the explanation for this?
Inspired= 0.4% Expired= 4%
This is because carbon dioxide is produced by respiration and dissolved from the plasma to the alveoli where it is expired
What is the % composition of nitrogen in inspired vs expired air
What is the explanation for this?
Inspired = 79% Expired = 79%
This is because nitrogen is neither absorbed nor used so all that is inhaled gets exhaled
What is the % composition of water vapour in inspired vs expired air
What is the explanation for this?
Inspired = variable Expired = saturated
This is because the water content of the atmosphere varies,
alveoli are permanently lined with moisture (surfactant) so water evaporates from them and is exhaled
Why do insects face a risk of dehydration
Because like terrestrial organisms they live in arid habitats where water can evaporate from their body surface
How do many terrestrial and insect organisms reduce water loss?
What is it made of?
Have a waterproof layer covering their body e.g the insect exoskeleton which is rigid and comprises of a thin wavy layer over a thick layer of chitin and protein
How does gas exchange occur in insects?
Through paired holes called spiralled running along the side of the body
What do the spiracles lead to in an insect?
Spiracles lead to a system of branched chitin lines air tubes called tracheae, which branch into smaller tubes called tracheoles
Why is it beneficial to line the tracheole walls with chitin?
Chitin is impermeable to water so water can’t evaporate across tracheole walls
How do spiracles reduce water loss?
Spiracles can open and close so gas exchange can take place and water loss can be reduced
Why is it benefits for spiracles to have hairs?
Hairs covering spiracles contribute to water loss prevention and prevent solid particles getting in
What gas exchange occurs in insects when resting
Diffusion through the spiracles where tracheae and tracheoles take in oxygen and remove carbon dioxide
During periods of activity with a high metabolic rate what gas exchange do insects rely on?
Rely on movements of the abdomen to ventilate the tracheae
Where does gas exchange take place in an insect?
The interface between tracheoles and muscle fibres
Why is it important for the ends of the tracheoles to be fluid filled and close to muscle fibres?
What does this mean?
To allow oxygen to dissolve In the fluid and diffuse directly into the muscle cells (opposite for co2)
-this means no respiratory pigment or blood circulation is required
LEARN DIAGRAM DOR TRACHEAL SYSTEM OF AN INSECT
LEARN DIAGRAM OF THE TRACGEOLE END INSIDE MUSCLE FIBRES
What limitations does the insect not having a circulatory system cause
Diffusion is only efficient over small distances, limiting the size of the insect
What gas exchange process do plants complete during the day?
Photosynthesis and respiration, as plant cells containing chloroplast have sunlight for photosynthesis
Where does the co2 required for photosynthesis come from?
Some comes from the products of respiration but most diffuses into the leaves from the atmosphere
What happens to the oxygen produced in photosynthesis
Some is used in respiration but most diffuses out of leaves
What forms of gas exchange occurs in plants at night?
Plants only respire not photosynthesis
How do plants gain oxygen for respiration at night
Some enters stem and roots by diffusion but most has exchange takes place at the leaves
LEARN DIGRAM ON PAGE 173
What is the overall product produced by plants during the day?
Explain.
Oxygen
Because the rate of photosynthesis is faster than the rate of reaction :: more oxygen is produced in photosynthesis than is used in respiration
What is the overall product produced by plants during the night?
Explain.
Carbon dioxide
At night photosynthesis doesn’t occur so no oxygen is produced
Name the important structures in a leaf
Cuticle Upper epidermis Palisade mesophyll cell Spongy mesophyll Lower epidermis Sub stomatal air chamber Stoma Guard cell Cuticle LEARN DIAGRAM ON PAGE 173
Why is the leafs diffusion pathway always short?
Because leaves are so thin
How do the gases diffuse through the stomata
Down a concentration gradient into the sub stomatal air chambers where they diffuse through the intracellular spaces between the spongy mesophyll cells and into cells
What maintains the diffusion gradients of oxygen/carbon dioxide between the inside and outside of a leaf?
Maintained by the mitochondria carrying out aerobic respiration and by chloroplasts carrying out photosynthesis
Define the term cuticle
Each covering on a leaf secreated by epidermal cells which reduces water loss
Why is the large surface area of a leaf vital for gas exchange and photosynthesis?
Gas exchange= room for many stomata
Photosynthesis= captures as much light as possible
Why is the thinness of a leaf vital for gas exchange and photosynthesis?
Gas exchange= diffusion pathway for gases entering and leaving is short
Photosynthesis= light can penetrate through leaf
Why is the air spaces In the spongy mesophyll vital for gas exchange and photosynthesis
Gas exchange= allows oxygen and carbon dioxide to diffuse between the stomata and the cells
Photosynthesis= allows carbon dioxide to diffuse to the photosynthesising cells
Why are stomatal pores vital for gas exchange
They allow for gas exchange in and out of the leaf through opening and closing
Name some more benefits for photosynthesis in a leaf
- cuticle and epidermis are transparent allowing light to penetrate the the mesophyll
- palisade cells are elongated to accommodate a large number
- palisade cells are packed with chloroplasts to capture as much light as possible
- chloroplasts rotate and move within mesophyll cells to be in the best positions for maximum light absorption
Define the term stomata/stomatal pore
Pore on a lower leaf surface, and other aerial parts of a plant, bounded by 2 guard cells, through which gases and water vapour diffuse
Describe guard cells
Only Epidermal cells with chloroplasts, also have unevenly thickened walls
Briefly describe thickness of stomatal cell wall
The inner cell wall next to the stomatal pore is thicker than the outer wall
Describe the mechanism In the stomata during the day
- if water enters the guard cells they become turgid and swell and the pores open
- if water leaves the guard cells they become flaccid and the pores close
Describe the steps that causes the stomatal pore to open (5)
- chloroplasts In guard cells photosynthesise producing ATP
- ATP provided energy for active transport of K+ ions into guard cells from surrounding epidermal cells
- stored starch (in starch grains) is converted to Malate
- stored K+ and malate ions lower water potential in guard cells making it more negative
- water enters by osmosis
- guard cells expand as the absorb water but less so in areas where the cell wall is thick causing guard cells to stretch and a pore appears
What is transpiration
A process where plants lose water by evaporation through their stomata
What happens if plants loose too much water?
They wilt
Why are stomatal pores positioned on the lower side of the leaf?
Because sunlight on the upper surface of the leaf would increase evaporation; so stomata on the lower minimises water loss
What other aspect of a leaf reduces water loss?
The waxy cuticle on the upper surface
When do stomatal pores close and why
- at night to prevent water loss when there is insufficient light for photosynthesis
- in very bright light, as this is generally accompanied by intense heat which would increase evaporation
- if there is excessive water loss
Why does only some of the air breathed in reach the gas exchange surface?
- air in the alveolus is stationary
- not all air inhaled passes out in the next expiration
- the inspired air has to change places with the alveolar air
